Graft polymers have been known for use in the coatings industry as binders for thermosetting compositions. Graft polymer binders typically have a plurality of functional sites reactive with the functional sites of one or more crosslinking agents and upon cure, produce hard, durable, glossy films suitable for use in a variety of coating applications. Preferred applications include automotive primers, basecoats, and clearcoats. Such coatings may be waterborne, solventborne, powder, or combinations thereof.
The manufacture of graft polymers has typically involved the production of a base material having one or more functional sites per molecule. At least one of these functional sites must be capable of subsequent or concurrent reaction with at least one functional group of a graft moiety.
Graft copolymerization processes have traditionally been used to incorporate moieties that cannot be incorporated during the preparation of the base material. Examples of such moieties include polymers such as polyesters, polyurethanes and the like, surfactants, halogenated compounds, certain water dispersible groups such as nonionic groups, simple alkyl groups, functional groups such as beta- and higher hydroxy primary carbamate groups, including gamma-hydroxy primary carbamate groups, delta-hydroxy primary carbamate groups, and the like, the derivatives thereof, acid functional materials, epoxy functional materials, silane functional materials, siloxane functional materials and the like.
However, numerous problems occur during such prior art graft reaction processes. In particular, in the processes of the prior art, the reaction of the graft moiety and the base material results in reaction products which are reactive with one or more species, including the base material, other intermediate species, and/or the graft moiety. Such undesirable side reactions result in uncontrolled molecular weight growth, the loss of desired functionality, and/or gelation.
In addition, the uncontrollable reactivity of the functional group used as the grafting site on the base material can often limit the use of additional functionality on the base material and hinder the production of multifunctional graft materials. As a result, it has been difficult to obtain certain multifunctional graft materials using the processes of the prior art.
For example, if an epoxy group is used as the grafting site on an acrylic backbone, ethylenically unsaturated monomers having functional groups reactive with epoxy must be avoided during the polymerization of the acrylic backbone if the epoxy group results from the use of an ethylenically unsaturated monomer such as glycidyl methacrylate. Illustrative functional groups that would have to be avoided include active hydrogen containing groups such as amine functional ethylenically unsaturated monomers, acid functional ethylenically unsaturated monomers, and depending, on the polymerization conditions, hydroxy containing ethylenically unsaturated monomers.
Assuming that an acrylic backbone polymer's functionality is limited to epoxy groups, the use of amine, hydroxy, or acid functional graft moieties will result in a variety of intermediate species which are reactive with the graft moiety, the epoxy functionality of the acrylic backbone or both. As a result, attempts to use an amine or acid functional graft moiety will often lead to uncontrolled molecular weight growth, the loss of desired functionality on the backbone, and/or gelation.
Moreover, it would be advantageous to obtain graft materials with the aforementioned advantages but which also comprise primary carbamate groups. Graft materials containing mixed functional groups such as β or higher-hydroxy primary carbamate groups would be even more advantageous.
It would thus be advantageous to provide a method of grafting that would address the deficiencies of the prior art. In particular, what is desired is a method of graft polymerization that would facilitate the production of multifunctional graft materials, especially multifunctional graft polymers wherein at least one functional group comprises a primary carbamate group, especially a β or higher-hydroxyl primary carbamate group. Such improved graft material manufacturing processes would have a decreased risk of uncontrolled molecular weight growth, the loss of desired functionality on the base material, and/or gelation.
It is thus an object of the invention to provide a method of making multifunctional graft materials that eliminates the disadvantages of the prior art.
In particular, it is an object of the invention to provide a method of obtaining a graft material having at least two functional groups that would be reactive with each other under reaction, oligomerization, or polymerization conditions. That is, the at least two functional groups on the final reaction product would normally present serious challenges with respect to side reactions if incorporated via traditional reaction, oligomerization or polymerization routes.
It is another object of the invention to provide a relatively simple and commercially feasible method of making β or higher-hydroxy primary carbamate functional materials having at least one other functional group obtained through grafting reactions, most particularly at least one hydroxyl functional urethanized grafting moiety.